The long-term objective of this research is to understand the thermodynamic states of biomembranes and how these relate to function in normal and pathological conditions. It is planned to investigate the presence or absence of subtransitions in several systems, including mixtures such as cholesterol-lipid, and in various LUV systems. LUVs, which approximate closely the unilamellar bilayer of cells, will be studied to determine the degree to which their overall thermodynamic properties are similar to the well characterized MLVs. The investigation of possible sub-critical phenomena will continue, including the effect of protein, cholesterol and second lipids. Various perturbations of the usual lipid bilayers will be examined to determine the effect of different parts of the lipid bilayer in contributing to the thermodynamic properties. Protein-lipid interactions of actin and D-lactate dehydrogenase will be investigated in reconstituted LUVs constructed from lipids designed to mimic the interior of the erythrocyte or E. coli membrane. The measuring techniques employed are dilatometry, using a state-of-the-art home built device, and differential scanning calorimetry, using a Microcal instrument which has been modified with a computer interface to enable measurements to be taken simultaneously of sharp transitions and low background single phase specific heats. These measurements together with elementary theory provide estimates of intermolecular interactions and the change in rotameric disorder.